A printing system has been designed which takes advantage of a spatial light modulator (SLM) to create a very simple exposure unit. The system uses a conventional light source such as a tungsten halogen light, and which is focused onto a spatial light modulator such as the deformable mirror device (DMD) consisting of a row or rows of individually deformable mirrors constructed on a single substrate.
The SLM is arranged in conjunction with a lens such that in the undeflected state, light reflecting from each mirror has a reflection angle such that the light is directed away from the remaining elements of the printing system. When a particular mirror is otherwise deflected, the angle of light reflection changes, and the light is then passed through the remaining system. The reflected light may, for instance, be directed to a photo receptor drum of a standard xerographic print process.
Present manufacturing processes are able to achieve SLM widths of up to 20 millimeters, containing approximately one thousand individual mirrors. These densities result in SLMs capable of illuminating a three-inch long strip at approximately 300 dots per inch (dpi) which is letter quality. Most printing applications, however, use formats wider than three inches. This requires a system designer to either lengthen the traditional 20 millimeter SLM row or to magnify the projected array such that a print density of less than 300 dpi results. The first alternative, producing an extended SLM, though theoretically possible, is prohibitively expensive. Producing a long SLM increases fabrication complexity of the SLM, poses difficult problems of uniform illumination, and often results in a nonuniform image even when properly illuminated. The second alternative, reducing the pixel print density, is not acceptable in those applications requiring letter quality print output.
Therefore, a need has arisen for a spatial light modulator system which is capable of illuminating an extended strip and which is easy to fabricate, illuminate and which results in uniform projections.